Pulse - June 2021 - 27

VETERINARY OPHTHALMIC CONSULTING QUICK REFERENCE
Anesthesia and Sedation:
Ophthalmic Considerations
Sara Calvarese, DACVO
Douglas Esson, DACVO
P
lanning perioperative care and anesthesia/
analgesia in the veterinary ophthalmic patient
presents special considerations. Many ophthalmic
patients present with unstable corneas/globes,
exhibit significant discomfort and/or will have delicate
surgical incisions post-operatively. Forceful
restraint, neck leads, significant extension of the neck
for jugular venipuncture, and even intubation (& jaw
opening) can be hazardous for a patient with a deep
corneal wound or fragile incision. Difficult mask or
box-inductions should also be avoided where possible.
The appropriate use of topical and/or local injectable anesthetic
agents may facilitate routine diagnostic and therapeutic
procedures. Be aware that the use of topical agents may
mask symptoms such as spastic entropion and may additionally
alter subsequent diagnostic information notably Schirmer
tear testing.
As with other surgical patients, minimizing stress and anxiety,
as well as pain, preoperatively benefits the patient and will
reduce the amount of induction agent and the level of maintenance
anesthetic required. Dexmedetomidine, diazepam/
midazolam, and acepromazine may be safely incorporated into
ophthalmic premedication plans. Opioids may also be safely
used in ophthalmic patients, providing both analgesia and
sedation. Premedication with Cerenia (maropitant) can minimize
nausea and vomiting and may also have analgesic effects.
Ketamine, however, may increase intraocular pressure, and the
use of this agent may be disadvantageous in some cases.
Some ophthalmic procedures can be safely performed
under injectable sedation/anesthesia.
Dexmedetomidine in combination with butorphanol, or
propofol alone (with proper airway/respiratory support if
needed) are adequate for selected minor procedures such as
corneal debridement/keratotomy, suture removal, simple conjunctival
foreign body removal, or even to facilitate thorough
ophthalmic evaluation in fractious or painful animals.
Routine induction with propofol, alfaxolone, or etomidate
is recommended for ophthalmic cases Maintenance anesthesia
with isoflurane or sevoflurane mixed with oxygen is standard.
Patients undergoing intraocular procedures will usually
require a neuromuscular blocking agent (atracurium,
rocuronium, pancuronium) to allow proper globe positioning
and minimize the risk of intraoperative complications.
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JUNE 2021
27
These patients will require mechanical ventilation and careful
and specific monitoring, as some of the usual reflexes used to
evaluate depth of anesthesia will not be present.
During ophthalmic procedures (notably enucleation), it is
important to be aware of the oculo-cardiac reflex (OCR),
which is a sudden reduction in heart rate associated with
traction on the extraocular muscles and/or compression of
the globe. The sensory afferent limb of the reflex is carried
by the trigeminal nerve to the CNS and the efferent limb
of the reflex is carried by the vagus nerve, which affects the
myocardium and the sinoatrial node potentially causing bradycardia,
arrhythmia, and in rare instances, arrest. Young animals
seem particularly susceptible to OCR, but it may occur
in any patient. The appropriate use of anti-cholinergic agents
can decrease the incidence of OCR.
The recovery period is a time for close monitoring, and
patient agitation, anxiety, and pain should be well managed
(notably using sedative and/or analgesic agents) to avoid postoperative
hemorrhage or damage to delicate incisions. Use of
an Elizabethan collar to prevent self-trauma is critical in postoperative
ophthalmic cases. P
VOC is independently and family owned with compassionate,
qualified and experienced team members. Doctors Esson and
Calvarese are Board-Certified Veterinary Ophthalmologists.
Pulse - June 2021

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